The Design Of Acquisition Module Of Acoustic Logging Tool

Acoustic logging tool is an indispensable key tool in petroleum logging technology.Its working principle is to use different transmitting transducers to excite the formation around the well,and use the corresponding receiving transducers to obtain the acoustic signal from the formation.The output signal of the receiving transducer is very weak,and the signal is easily drowned by the noise because of the bad working environment in the well.Therefore,the design of the signal acquisition module needs to focus on its signal-to-noise ratio index and anti-interference ability.Only the acquisition module with high signal-to-noise ratio can meet the resolution and measurement accuracy requirements of acoustic logging tool.In this paper,the structure,working principle and working flow of the acoustic logging tool are investigated,and the function of the signal acquisition module is defined.Then,the signal acquisition module is composed of four strip circuits with the same structure.The strip circuit mainly consists of 12 channels and digital interface circuits.The main function of the channel circuit is to receive,amplify,filter and digitize the acoustic signal,which is composed of signal conditioning circuit and A/D conversion circuit.The channel circuit can produce the output of the self-test signal under the excitation of the square wave test signal with 9 different frequencies.The self-test signal can reflect the capacitance change of the receiving transducer.In order to design a signal receiving circuit with high signal-to-noise ratio,it is necessary to analyze the internal noise and external interference of each circuit module of the signal acquisition module.Through the combination of simulation and calculation,the noise power of each part of the circuit is analyzed,and the method to reduce the external interference is proposed.The output signal of the signal conditioning circuit is converted to digital signal by A/D converter.The digital interface circuit realizes the synchronous acquisition and serial transmission of A/D conversion data of 12 channels in one strip.The synchronous clock error is less than 0.1?s.Serial transmission is realized by LUDS high-speed differential interface.In order to verify the performance index of the signal acquisition module,an independent test platform is designed,which includes test equipment and test software.The test platform receives the collected data according to a given protocol and transmits it to a computer for storage and analysis.Finally,a series of tests are carried out to verify the performance index of the channel circuit and the whole function of the signal acquisition module.The circuit function test is mainly to verify whether the actual index of the channel circuit is in line with the design expectation,and the noise test and analysis are used to measure and calculate the signal-to-noise ratio index of the circuit.The various functional indicators of the signal acquisition module are quantitatively analyzed.The main technical indexes meet the requirements of the client.The designed signal acquisition module has been delivered and accepted.